1. Field of the Invention
Embodiments of the invention relate to an organic light emitting display. More particularly, embodiments relate to an organic light emitting display that may suppress image sticking due to a decrease in efficiency of an organic light emitting diode and may compensate for a threshold voltage of a driving transistor.
2. Description of the Prior Art
In general, an organic light emitting display is a display that emits light by electrically exciting a fluorescent or phosphorescent compound. The organic light emitting display may display an image by driving N×M organic light emitting diodes (OLEDs). Each OLED may include an anode electrode (indium tin oxide (ITO)), an organic thin-film layer, and a cathode electrode (metal). To improve light emission efficiency and a balance between electrons and holes, the organic thin-film layer may have a multi-layer structure including an emitting layer (EML), an electron transport layer (ETL) and a hole transport layer (HTL). The organic thin-film may include a separate electron injecting layer (EIL) and a hole injecting layer (HIL).
In general, the anode electrode is coupled to a first power supply to supply holes to the EML, and the cathode electrode is coupled with a second power supply to supply electrons to the EML. The second power supply has a lower voltage than the first power supply. Thus, relative to cathode electrode, the anode electrode has a positive (+) electric potential and, relative to the anode electrode, the cathode electrode has a (−) electrode potential.
The HTL accelerates hole(s) supplied from the anode electrode and supplies the hole(s) to the EML. The ETL accelerates electron(s) supplied from the cathode electrode and supplies the electron(s) to the EML. As a result, at the EML, the electron(s) supplied from the ETL and the hole(s) supplied from the HTL may recombine with each other, thereby generating a predetermined amount of light. The EML layer may include organic material that may generate one of red light, green light and blue light when the electron(s) and hole(s) recombine therein.
In such OLEDs, because a voltage applied to the anode electrode is always higher than a voltage applied to the cathode electrode, negative (−) carriers are positioned on the anode electrode, and positive (+) carriers are positioned on the cathode electrode. If the negative (−) carriers positioned on the anode electrode and the positive (+) carriers positioned on the cathode electrode are maintained for a long time, movement of electron(s) and hole(s) may decrease. Thus, efficiency of the OLED(s) may decrease the more the OLED(s) is used. As a result, image sticking may occur and a life span of the OLED(s) may be shortened.